Multiple Image Collection and Synthesis for Personnel Screening

ABSTRACT

An apparatus and method for inspecting personnel or their effects. A first and second carriage each carries a source for producing a beam of penetrating radiation incident on a subject. A positioner provides for synchronized relative motion of each carriage vis-á-vis the subject in a direction having a vertical component. A detector receives radiation produced by at least one of the sources after the radiation interacts with the subject.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/272,056, filed Nov. 17, 2008, and like thatapplication, the present application claims priority to U.S. ProvisionalApplication No. 60/998,933, filed Nov. 19, 2007.

U.S. patent application Ser. No. 12/272,056 is a continuation-in-partapplication of U.S. patent application Ser. No. 11/737,317, filed Apr.19, 2007 and issued Mar. 17, 2009 as U.S. Pat. No. 7,505,562. Thepresent application, like application Ser. Nos. 12/272,056 and11/737,317, claims priority to U.S. Provisional Application No.60/794,295, filed Apr. 21, 2006.

U.S. patent application Ser. No. 12/272,056 is also acontinuation-in-part application of U.S. patent application Ser. No.12/171,020, filed Jul. 10, 2008 and issued Sep. 22, 2009 as U.S. Pat.No. 7,593,506. application Ser. No. 12/171,020 is a continuationapplication of U.S. patent application Ser. No. 11/097,092, filed Apr.1, 2005 and issued Jul. 15, 2008 as U.S. Pat. No. 7,400,701. The presentapplication, like application Ser. Nos. 12/272,056, 12/171,020 and11/097,092, claims priority to U.S. Provisional Application No.60/561,079, filed Apr. 9, 2004.

All of the foregoing applications and patents are hereby incorporated byreference herein in their entireties.

TECHNICAL FIELD AND BACKGROUND ART

The present invention relates to the field of x-ray imaging ofpersonnel, packages, or other subjects to detect concealed objects.

Current personnel screening systems using backscatter and millimeterwave technology can provide images representative of the surface of thescanned subject, but, insofar as they may well not penetrate theentirety of the scanned subject, they lack the capability to image itemsof interest located on the far side of the subject, or items of interestthat return a signal response similar to the background surrounding thesubject, or items artfully concealed on the subject.

In an attempt to increase the detection accuracy of such screeningsystems, additional scans are required that might further necessitaterepositioning the subject to be scanned. These additional scanningrequirements, while possibly increasing detection accuracy,significantly reduce the rate of throughput of such systems that aregenerally implemented under circumstances that experience large volumesof scanning.

A system that provides both accurate and effective imaging at a highthroughput rate and requires inspected subjects to be exposed to only alow dose of radiation is particularly desirable in such applications.

Accordingly, the present invention is directed toward providing anapparatus and method of scanning that can achieve these desiredobjectives.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the present invention anapparatus is provided that ascertains a material feature associated witha subject, and in certain embodiments, generates one or more images ofthe subject. The apparatus generally includes a first carriage, a secondcarriage, at least one vertical positioner, and at least one detector.Each carriage includes a source that is adapted to produce a beam ofpenetrating radiation incident on the subject. The vertical positioneris adapted to synchronously displace each carriage with respect to thesubject in a direction having a vertical component. The at least onedetector receives radiation produced by at least one of the sourcesafter interaction of the radiation with the subject. The detector may bedisposed on the first carriage. The subject may be a person.

The penetrating radiation produced by each source may be in the form ofx-ray radiation. Each source may be adapted to produce a pencil beam ofradiation. Each source may also have a scanner adapted to move the beamof penetrating radiation produced by the source transverse to thedirection of motion of the carriages. Each scanner may be in the form ofa chopper wheel and the chopper wheel may be adapted to provideinterleaved beams.

Each carriage may include a plurality of detectors. Each plurality ofdetectors may include at least one of a scatter and transmissiondetector.

The first and second carriages may produce substantially oppositelydirected beams of penetrating radiation.

The transmission detector of the first carriage may be disposed at anelevation substantially equal to that of the source of the secondcarriage.

In one embodiment of the present invention the first and secondcarriages may be structurally coupled. Both carriages may be coupled toa single mechanical platform wherein the at least one positioner isadapted to move the single mechanical platform in a direction having avertical component.

In another embodiment of the present invention each source may be anintermittently irradiating source providing a temporally interlacedirradiation pattern.

An embodiment of the present invention may include a displacementencoder.

The positioner of the apparatus may include at least one of a rotarymotor coupled to a lead screw, a rack and pinion system, anelectromechanically propelled system, a hydraulic piston or a pulleysystem in accordance with an embodiment of the present invention.

The apparatus may include a processor for receiving a signal from the atleast one detector and for producing an image based at least on thesignal and may further include a processor for electronically combiningthe images produced by each detector in one embodiment.

In accordance with a related embodiment of the present invention theapparatus may include an enclosure for containing the carriages and theat least one positioner during the course of operation. At least onestationary detector may be coupled to the enclosure. The enclosure maybe an environmentally controlled enclosure. The enclosure may besealable from an external environment.

In an embodiment of the present invention each source may be a pulsedsource adapted to intermittently irradiate the subject.

In accordance with another embodiment of the present invention anapparatus for ascertaining a material feature associated with a subjectis provided that includes a first carriage, a second carriage and atleast one vertical positioner. The first carriage includes a sourceadapted to produce a beam of penetrating radiation incident on thesubject and a first detector for detecting penetrating radiationscattered by the subject. The second carriage includes a second detectorfor detecting penetrating radiation produced by the source of the firstcarriage and transmitted through the subject. The at least one verticalpositioner is adapted to synchronously vary the position of eachcarriage with respect to the subject in a direction having a verticalcomponent. The positioner may act on the first carriage to vary therelative position of the source on the first carriage with respect tothe subject.

In accordance with another embodiment of the present invention anapparatus is provided for ascertaining a material feature associatedwith a subject. The apparatus includes two vertically disposed arrays ofsources adapted to produce beams of penetrating radiation, at least onedetector for receiving radiation produced by at least one of the sourcesafter interaction of the radiation with the subject, and a controllerfor activating at least one source in at least one of the arraysindependent from the other sources in the same array.

In a related embodiment the at least one detector of the apparatusincludes two vertical arrays of detectors and a processor for processingdetection data received by each detector during a specified timeinterval.

In another related embodiment the apparatus includes a scanner adaptedto move at least one beam of penetrating radiation produced by at leastone of the sources.

In accordance with another embodiment of the present invention a methodis provided for inspecting a subject. The method has steps of: moving afirst carriage having coupled to it a first source adapted to produce abeam of penetrating radiation incident on the subject, moving insynchronization with the first carriage a second carriage having coupledto it a second source adapted to produce a beam of penetratingradiation, detecting with at least one detector radiation produced by atleast one of the sources after interaction of the radiation with thesubject, generating detector output signals based on radiation receivedby the at least one detector, and characterizing the subject on thebasis of the detector output signals. The at least one detector may becoupled to at least one of the first carriage and the second carriage.

In a related embodiment the method further includes scanning the beam ofpenetrating radiation produced by the source in a direction transverseto the direction of motion of the carriages.

In another related embodiment the method further includes creating animage based on radiation detected by the first and second detectors.

In yet another related embodiment the method include the steps of:scanning the beam of penetrating radiation produced by the sourcecoupled to the second carriage in a direction transverse to thedirection of motion of the carriages, generating detector output signalsbased on radiation received by the first and second detectors andcreating an image based on radiation detected from the first and thesecond beam. In any of the described methods for inspecting a subjectthe subject may be a person.

In accordance with another embodiment of the present invention a methodis provided for inspecting a subject. The method includes generatingbeams of penetrating radiation at a temporally varying elevation, thebeams of penetrating radiation generated by at least one first sourcepositioned to direct the radiation in a first direction toward thesubject and at least one second source positioned to direct penetratingradiation in a second direction toward the subject and detecting with atleast one detector the radiation produced by at least one of the sourcesafter interaction of the radiation with the subject. The at least onefirst source may comprise a first plurality of sources disposed atdistinct vertical heights and the at least one second source maycomprise a second plurality of sources at distinct vertical heights.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention relates to the field of screening cargo or anyother packages and/or subjects.

The foregoing features of the invention will be more readily understoodby reference to the following detailed description taken with theaccompanying drawings:

FIG. 1 is a schematic view of an embodiment of the present inventionused to scan a person who has entered the imaging apparatus.

FIGS. 2A and 2B are illustrations of a lead screw type positionerattached to a carriage of the current invention.

FIG. 3 is a top view of two sources and two chopper wheels configuredsuch that the sources may alternately scan a subject in accordance withan embodiment of the present invention.

FIG. 4 illustrates an inspection system provided within an enclosure, inaccordance with certain embodiments of the present invention.

FIG. 5 is a schematic depiction of a prior art x-ray source based onelectron field emission.

FIG. 6 shows the use of a single-dimensional array of discrete sourcesin a backscatter imaging application, in accordance with an embodimentof the present invention.

FIG. 7 shows the use of a two-dimensional array of discrete sources in abackscatter imaging application, in accordance with an embodiment of thepresent invention.

FIG. 8 shows the use of a single-dimensional array of discrete sourcesand a fixed set of backscatter detectors in a backscatter imagingapplication, in accordance with an embodiment of the present invention.

FIG. 9 shows an image generation apparatus in which multipleone-dimensional source arrays are mounted on a single cylinder, inaccordance with an embodiment of the present invention.

FIG. 10A shows a front view of an embodiment of the present invention inwhich x-rays are emitted from above.

FIG. 10B shows a schematic side view of an embodiment of the presentinvention, depicting a person at successive positions traversing aplurality of x-ray beams emitted from above.

FIG. 11A shows a front view of an embodiment of the present invention inwhich x-rays are emitted from opposing sides.

FIG. 11B shows a schematic side view of an embodiment of the presentinvention, depicting a person at successive positions traversing aplurality of x-ray beams emitted from above.

FIG. 12 shows a schematic cross sectional view of an x-ray inspectionsystem that uses multiple backscatter imaging systems in accordance withembodiments of the present invention.

FIG. 13 shows a side view of the x-ray inspection system embodiments ofFIG. 12.

FIG. 14 shows a prior art backscatter system employing anelectromagnetic scanner of a sort employed in various embodiments of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Definitions. As used in this description and the accompanying claims,the following terms shall have the meanings indicated, unless thecontext otherwise requires:

A “carriage” is a moveable system including a source and/or a detectorof penetrating radiation. A carriage may include a detector that detectsradiation; however, it is not required to.

A “vertical positioner” is a system component capable of displacing acarriage in a direction having a vertical component. A positioner mayinclude an actuator, such as a motor, and attendant mechanical linkagesor couplings.

A “vertically disposed array” is a plurality of objects, generallysources or detectors, disposed in a configuration having a verticalcomponent such that at least one source in a vertically disposed arrayof sources is at a different elevation than at least one other source inthe same vertically disposed array.

FIG. 1 is a schematic view of an embodiment of the present inventionscanning a person who has entered a vicinity of the imaging apparatus.The imaging apparatus, illustrated in FIG. 1, and designated generallyby numeral 10, uses two distinct sources that produce penetratingradiation so that the subject is scanned, in a single pass, and isimaged from two opposite sides, thereby enabling effectiveidentification of any concealed objects. The penetrating radiationproduced by each source is typically electromagnetic radiation, such asx-rays or sub-millimeter-wave radiation; however, under certaincircumstances, the use of either electromagnetic radiation in otherfrequency ranges or of entirely different particles, such as baryons,may be advantageous. The sources are distinct in that they allow a beamof penetrating radiation to be produced from each carriage to facilitateimaging the subject. Various images may be produced including imagesbased on transmission and/or scatter radiation detected on either sideand/or top of the subject. These images may be producedcontemporaneously. The contemporaneously produced images may be combinedusing any processing methods. Source 102 of the apparatus is coupled tocarriage 100. Carriage 100 may include one or more detectors. Threedetectors are shown for illustrative purposes. The three detectorsillustrated include detector 104, configurable for forward scatterdetection, detector 106, configurable for transmission detection, anddetector 105, also configurable for forward scatter detection. It willbe appreciated by those of ordinary skill in the art that carriages arenot limited to including three detectors or a specific type of detector.Particularly, each detector may be configured to detect more than oneform of radiation. A carriage may include one or more detectors and anysingle detector on the carriage may be configured to serve as a forwardscatter, transmission, or backscatter radiation detector.

Configuring a detector to sense a particular kind of radiation may beachieved by modifying the detectors output, detection period, and/orsensitivity level. For example, each detector may output detectedinformation to a processor specifically configured to process thedetected signal. Further, the processor configuration may alternatedepending on what type of radiation is detected during any given timeinterval. The detectors may be configured, for example, so that duringthe course of the time interval during which source 102 is producing abeam of radiation, detectors 104, 105, and 106 are configured to detectbackscatter radiation, detectors 114 and 115 are configured to detectforward scatter radiation, and detector 116 is configured to detecttransmission radiation. In the same example the detectors may beconfigured such that during the course of another time interval, definedby source 112 producing a beam of radiation, detectors 114, 115, and 116are configured to detect backscatter radiation, detectors 104 and 105are configured to detect forward scatter radiation, and detector 106 isconfigured to detect transmission radiation. This is just a singleexample of how the detectors may be configured to operate and theconfiguration is amenable to the provided system components andparticular application. As such, various configurations, which may notbe explicitly described may be provided in accordance with embodimentsof the present invention.

Carriage 110, similar to carriage 100, includes three detectors that arecoupled to it. The three detectors coupled to carriage 110 includedetector 114 configurable to detect forward scatter radiation, detector116 configurable to detect transmission radiation, and detector 115 alsoconfigurable to detect forward scatter detection. These detectors, asthose on carriage 100, may each be configured, as discussed in theexample above, to detect each type of radiation, including forwardscatter, transmission, and/or backscatter radiation.

Carriages 100 and 110 are each maintained at substantially the sameelevation throughout a scan. Carriages 100 and 110 are generally eachcoupled to separate vertical positioners that move the carriages alongthe trajectory illustrated by lines 108 and 118 respectively, as furtherillustrated in FIG. 2A. The positioners move the carriages in agenerally vertical direction at the same rate such that the carriagesmaintain a substantially equivalent elevation relative to one anotherthroughout the displacement of each carriage. The scanning systemillustrated further includes a stationary side scatter detector 122 thatdetects radiation scattered approximately vertically during a scan.

As the source illustrated in FIG. 1 scans subject 120 horizontally,simultaneous to the carriages being displaced vertically insynchronization with one another, the radiation produced from a firstsource that is located on a first carriage may be detected, afterinteraction of the radiation with the subject, by detectors located onan opposing second carriage. Additionally, the radiation produced from asecond source located on a second carriage may be detected, afterinteraction of the radiation with the subject, by detectors located onthe opposing first carriage. The type of radiation detection may includetransmission and or scatter detection. Although backscatter detectorsare not expressly demonstrated on the carriages in FIG. 1, the carriagesmay include detectors configured to detect backscatter radiation. In anembodiment in which a detector is configured to detect backscatterradiation, the detector may detect radiation produced from a sourcelocated on the same carriage as the detector, as explained in theexample above.

In a preferred embodiment the source of each carriage may be adapted toproduce pencil beam x-rays. This may be achieved through the use of acollimator or by any means of producing a narrow beam of penetratingradiation. The source may be further adapted in a preferred embodimentto scan a subject in a direction transverse to the generally verticaldirection of travel by the carriage. The scanning may be achieved usingdevices including, but not limited to, chopper wheels, electromagneticsteering devices, or any other scanning systems.

FIG. 1 also illustrates the relative positions of the detectors on onecarriage with respect to the source on an alternative carriage,specifically for the configuration of sources and detectorsdemonstrated. In the embodiment illustrated in FIG. 1, each source islocated at a position that corresponds to the height or elevation of theopposing detector that is configurable for transmission detection.Specifically, detector 116 of carriage 110 is at substantially the sameelevation as source 102 on carriage 100 and vice versa for source 112 oncarriage 110 and detector 106 on carriage 100.

Two of the detectors configurable to detect forward scatter radiation oneach carriage are disposed, in an embodiment, at a vertically offsetdistance from the corresponding source, such that the scatteredradiation that results from the beam of penetrating radiation incidenton the subject is detected. Although detector 106 may be configured todetect scatter radiation, detectors 104 and 105 may be more optimal thandetector 106 at detecting forward scatter radiation resulting from thebeam of source 112 interacting with a subject disposed between thecarriages. Similarly, detector 116 may be configured to detect forwardscatter radiation, but detectors 114 and 115 may be more optimal thandetector 116 at detecting forward scatter radiation resulting from thebeam produced by source 102 interacting with a subject due to thevertical offset of detectors 114 and 115 from source 102.

To achieve coordinated motion of the carriages, structural coupling thatallows the carriage to move as a single body may be provided.

In use, a subject enters a vicinity of the inspection system and thenthe carriages are displaced vertically as the subject is scanned from atleast two sides in a single pass. As a new subject enters the portal forscanning, the carriages can begin scanning the subject from theircurrent position as they are displaced vertically in the oppositedirection of displacement performed in the previous scan. For example,one subject is scanned as the carriages are displaced in a verticaldirection decreasing in elevation and after the scan is completed andthe next subject enters, the next subject may be scanned as thecarriages are displaced in a vertical direction increasing in elevation.

In another embodiment of the present invention each carriage may includea source without any detectors coupled to the moveable carriage. Forexample, carriages 100 and 110 may each be provided without any ofdetectors 104, 105, 106, 114, 115, and 116. In this example, stationarydetectors may be provided that detect transmission and/or scatterradiation as the carriages are displaced and the sources alternateactivation. The stationary detectors in this example may still beconfigurable. The stationary detectors may also be provided, forexample, in an array that extends approximately the length of travel ofthe carriages, thereby allowing them to detect radiation similar to thedetectors attached to the carriages illustrated in FIG. 1.

While FIG. 1 generally illustrates each carriage as having a source, itis within the scope of the current invention to provide a source on onlyone of two carriages and to provide a scatter detector on the samecarriage as the source, and a corresponding transmission or forwardscatter detector on the oppositely disposed carriage. Alternatively, theapparatus illustrated in FIG. 1 could operate with only one source onone carriage producing penetrating radiation and the oppositely disposedcarriage solely detecting radiation produced by that carriage as subject120 is imaged.

FIG. 2A is an illustration of a lead screw type positioner attached to acarriage of the current invention. The imaging apparatus illustrated inFIG. 2A, designated generally by numeral 11 shows lead screws 200 and210 coupled to carriages 100 and 110 such that as the rotary lead screwmotors 201 and 202, here serving as the positioners, are operatedsimultaneously, carriages 100 and 110 move in a generally verticaldirection along the axis of rotation of their respective lead screws.This figure illustrates one type of positioner that may be implementedwith carriages of the current invention to achieve the necessarydisplacement; however, embodiments of the present invention mayincorporate other systems that can be used to achieve displacement ofthe carriages. These systems may include, but are not limited to, a rackand pinion system, an electro-mechanical system, which may useelectro-magnetism propulsion, a hydraulic system, or a pulley system.The invention also contemplates displacing the carriages by a singlepositioner that is coupled to the carriages. The positioner may includea single positioner having a mechanical platform coupled to more thanone carriage. The positioner may, alternatively or additionally, includea system that allows motion of the carriage or carriages in a directionor directions other than a vertical direction. Any of the systemsdescribed, or any other positioner used, may be commanded by acontroller that includes a displacement encoder 212 to providedisplacement of the carriages to a specified position or over aspecified displacement. The controller might further command the rate atwhich the displacement is achieved or any other relevant variablespertaining to carriage movement.

In one embodiment the positioner may be coupled to a displaceable memberthat subject 120 may be disposed on, as opposed to the positioner beingcoupled to the carriages. In the embodiment where the positioner isattached to a displaceable member that subject 120 may be disposed on,for example a mechanical platform located between two carriages, thepositioner may vary the height of the member in a direction having avertical component such that the subject or some region of the subjectis scanned by the carriages. In this embodiment the same images producedthrough moving the carriages in synchronization in a direction having avertical component are achieved because both embodiments provide for avariation in the relative orientation of the subject with respect to thecarriages, while maintaining each carriage at an elevation that does notchange with respect to the other carriage.

FIG. 2B is a profile view of an embodiment of the present invention usedto scan a person who has entered the imaging apparatus. As previouslyindicated, the sources may be offset from one another such that eachsource is located at a position that corresponds to the height orelevation of the opposing detector that is configurable for the requiredtype of detection. For example, a detector configurable for transmissiondetection being located at a vertical height on one carriage that iscommensurate with the source located on an oppositely disposed carriage.The imaging apparatus, designated generally by numeral 12 in FIG. 2Bshows that offsetting the sources, here source 252 and source 262, maybe achieved by offsetting the corresponding carriages, here carriages250 and 260. For example if the carriages were similarly configured withthe source centrally located and producing a beam of penetratingradiation from a central location on the carriage, each carriage couldbe coupled to the respective positioner at an elevation whereby onecarriage is vertically offset from the other carriage such that therespective source of each carriage is vertically offset with respect tothe source of the other carriage. This setup still effectuates the useof configurable detectors as previously discussed. Particularly, duringthe time interval when source 252 is activated detectors 253 and 254 maybe configured to detect backscatter radiation, detector 264 may beconfigured to detect transmission radiation, and detector 263 may beconfigured to detect forward scatter radiation. Further, during thetimer interval when source 262 is activated detectors 263 and 264 may beconfigured to detect backscatter radiation, detector 253 may beconfigured to detect transmission radiation, and detector 254 may beconfigured to detect forward scatter radiation.

FIG. 2B further illustrates lead screws 251 and 261 that providecarriages 250 and 260 with motion in a generally vertical direction asthe lead screws are rotated by motors 255 and 265.

FIG. 3 is a top view of two sources with chopper wheels configured suchthat the sources may alternate producing radiation that is incident onthe subject. The imaging apparatus is designated in FIG. 3 by numeral13. The invention encompasses adapting the sources to produce radiationincident on the subject at distinct time intervals. This may be achievedwith a steady state transmitting source or with a pulsed source thattransmits radiation during distinct time intervals. In the event that asteady state transmitting source is used, the source may be providedwith a chopper wheel that has one-half the normal number of slits, forexample. The apparatus will thus be provided with a controller adaptedto synchronize the sources irradiation of a subject such that thesources alternate producing radiation incident on the subject duringspecified time intervals in order to achieve full width scans on bothsides of the subject, simultaneous to the carriages being disposed insynchronization in a generally vertical direction, by the positioners orpositioner.

In FIG. 3, a first and second carriage 300 and 310 are shown from a topview. The carriages each illustrate a source 301 and 311 producingpenetrating radiation 302 and 312. The penetrating radiation may beproduced in a range dictated by the source used, and is not intended tobe limited by the illustration. The range of the source is determinativeof the range through which the beam of radiation is scanned or swept.This range is illustrated by lines 315 and lines 305. Lines 315represent the range or window through which a beam produced by source311 is swept. Lines 305 represent the range or window through which abeam produced by source 301 is swept. The subject is placed between thecarriages as illustrated by marker 320 for scanning The sources producea beam of radiation that is swept by the chopper wheels 304 and 314. Thechopper wheels include openings 303 and 313 that allow the penetratingradiation produced by the respective sources to be emitted through theopenings as the wheels move in a generally rotary motion. The rotationof the chopper wheels may include full 360 degree rotations or less. Therotation of the chopper wheels may also include an oscillating rotationor any other motion that allows the radiation to be scanned. The wheelsare designed to effectively shield the radiation emitted from the sourceon an interval during which any of the openings 303 and 313 are not infront of the direction of radiation emission from their respectivesources. As such the wheels may be constructed of lead or any othersuitable material that effectively shields the radiation produced by thesource used. As shown in the figure, beam 316 begins sweeping throughrange 315 simultaneous to chopper wheel 304 shielding radiation 302produced by source 301. The beams will continue to alternate being sweptas the carriages are moved in a vertical direction, into or out of theplane of the page, in order to achieve a complete scan of the subject.Alternative configurations may be provided that allow differentinterleaved irradiation schemes.

FIG. 4 is an illustration of the inspection system provided within anenclosure for containing the carriages and the at least one positionerduring the course of operation. The enclosure 450 may include a portal451 that a subject may enter for scanning The enclosure may be providedin a mobile form. The enclosure illustrated is provided with carriages400 and 410 that may contain the desired detector source combinationrequired for the specific scanning application. These carriages aredisplaced in a generally vertical direction. The enclosure 450 may alsoinclude a stationary scatter detection system, such system 451. Theenclosure may include stationary detectors located on the top, bottom,or any other sides of the container. The information obtained from eachof these detectors may be viewed or processed individually or theinformation may be processed and combined with the information fromanother detector or detectors, including the detectors located on acarriage in order to obtain greater details about a concealed object ofinterest located on a scanned subject. The enclosure may also includeonsite inspection controls and an analysis system or the enclosure maybe adapted for use with a remote analysis system. The enclosure mayprovide for environmental control so that the internal temperature,humidity, air pressure, microbial or contaminant content, or otherenvironmental factor may be regulated. The enclosure may seal aninterior portion of the enclosure from the surrounding outsideenvironment.

Some embodiments of the present invention may relate to methods andsystems for inspecting objects by means of penetrating radiation thatuse multiple x-ray sources, which may be individually activated, asdescribed in U.S. Patent Application Publication No. 2007/0258562,hereby incorporated by reference herein in its entirety.

X-ray sources may be based on field-emission cathodes, offeringadvantages in both spatial and temporal resolution when compared withthermionic sources. Because field emission of electrons is produced by ahigh electric field, no heating is necessary, whence such electronemitters are commonly referred to as cold cathodes. The electron beamsemitted by such devices may have low divergence and thus provide ease offocusing. Moreover, the virtually instantaneous response of the sourceoffers time gating capabilities comparable with the time resolution ofthe control circuit, and may be as fast as nanoseconds, using currenttechnology.

Zhang et al., A Multi-beam X-ray Imaging System Based on Carbon NanotubeField Emitters, in Medical Imaging 2006, (Proceedings of SPIE, Vol.6142, Mar. 2, 2006), reported the fabrication, by Xintek, Inc. ofResearch Triangle Park, N.C., of a linear array of 5 X-ray sources, eachwith a focal spot between 200 and 300 μm, based on the use of carbonnanotube (CNT) electrodes. Electron currents in the range of 0.1-1 mAwere reported at an accelerating voltage of 40-60 kVp. The lifetime ofthe cold cathode was estimated to exceed 2000 hours. For an acceleratingvoltage of 200 kV, a beam current of 13 mA has been measured. Theaforesaid Zhang et al. paper is incorporated herein by reference.Devices with 1000 pixels per meter and pulse repetition rates on 10 MHzcan be envisioned with technology within the current state of the art.

The use of CNT cold cathodes in the context of an x-ray source is alsodescribed by Cheng et al., Dynamic radiography using acarbon-nanotube-based field-emission X-ray source, 75 Rev. Sci.Instruments, p. 3264 (2004), while the use of CNT cold cathode sourcearrays in a scanning context is described by Zhang et al., Stationaryscanning x-ray source based on carbon nanotube field emitters, 86 Appl.Phys. Lett., p. 184104 (2005), both of which articles are incorporatedherein by reference.

Moreover, the use of CNT cold cathode source arrays in tomography isdiscussed by Zhang et al., A nanotube-based field emission x-ray sourcefor microcomputed tomography, 76 Rev. Sci. Instruments, p. 94301 (2005),which is also incorporated herein by reference.

Discrete cold cathode sources may advantageously provide forelectronically turning on the sources, and with low latency (on thenanosecond scale), in a sequential manner, thereby forming pencil beams,as often practiced in the x-ray imaging arts, or, alternatively,selecting a pattern of sources at a given time to form coded beams. Thedevelopment of CNTs has allowed important technical challenges relatedto current stability and cathode life time to be overcome.

The general operation of a cold cathode x-ray source, designatedgenerally, in FIG. 5, by numeral 1010, is well understood in the art andis described with reference to FIG. 5. The cold cathode arrangementadvantageously allows for a high degree of control. Voltage V_(ge)between gate 1012 and cathode 1014, governed by control circuit 1013,controls the current of electrons 1015, while voltage Y_(ca) betweencathode 1014 and anode 1016, which also serves as the X-ray target,controls the electron energy impinging on the target 1016, and thevoltage applied on the focusing electrode 1018 determines the electronbeam spot size.

While FIG. 5 depicts an assembly in which the x-rays are generated via areflection target 1019, a transmission target may also be employedwithin the scope of the present invention.

Application of discrete x-ray sources for x-ray imaging, in accordancewith the present invention, varies with the dimensionality of the x-raysource array (one-, two-, or three-dimensional), the scanning mode(raster or pattern), the dynamic use of different or varying energies,and the use of time gating.

An embodiment of the invention is described with reference to FIG. 6. Aone-dimensional array 1020 of x-ray sources 1022 is disposed withbackscatter detectors 1023 on one or more sides of its longitudinal(typically vertical) axis 1021. The entire device 1024 can translate ina transverse direction 1025, typically horizontally, so as to create animage on a line-by-line basis. Alternatively, array 1020 may rotateabout longitudinal (typically vertical) axis 1021 such that x-ray beam1026 sweeps in a transverse direction (again, typically horizontally),thereby creating a line-by-line image, but without the entire devicemoving. An image line is created by raster scanning the sourcesvertically by turning on one source 1022 at a time in rapid succession.

Referring now to FIG. 7, a two-dimensional source array 1030 may have nomechanically moving parts and allow coverage of a predefined solid angle(determined by the total number of sources 1032 and their divergence) ina very short time. It can use a raster scan mechanism similar to a CRTor pattern beams (Hadamard or other coding mechanism).

In accordance with further embodiments of the present invention, asystem with controlled velocity, designated generally by numeral 1040,is described with reference to FIG. 8. One or more backscatter detectors1042 are fixed, but the source array 1044 is translated with a constantspeed back and forth in direction 1045 adjacent to, or between,detectors 1042. Such system may also be employed in an interlaced mode,described below.

Further versatility may be achieved using a related embodiment such asthat shown in FIG. 9 where two or more one-dimensional x-ray sourcearrays 1051, 1052, are mounted on a cylinder 1054. Because the arrayscan be turned on and off electronically with high speed, only the arraygenerating an x-ray beam 1055 that is illuminating a target (not shown)is turned on, and the other arrays are off, hence there is no need toshield one array from another. The versatility of this model resides inits natural ability to incorporate the interlaced mode, as nowdescribed, and to continuously accumulate an image. Alternatively twocylinders could be provided to produce radiation incident on two sidesof a subject. The sources in each array may be provided with acontroller for independent activation of the sources.

Interlacing can be useful in cases where, due to technical limitationsor by design, the minimum distance between two sources is 1 cm, but therequired resolution for a specific applications demands sources placed 4mm apart. On a cylinder, three one-dimensional arrays are placed at 120degrees one from another and shifted vertically by 3.33 mm. Each arraywill scan lines 1 cm apart, but because of the vertical shift, theresulting image for a complete rotation of the cylinder will have aresolution of 3.33 mm. This mode of operation is referred to as“interlaced mode.” For the system depicted in FIG. 8, interlaced imagingmay be provided via vertical translation of the array for eachhorizontal pass.

In accordance with further embodiments of the present invention, carbonnanotube x-ray sources configured in a linear or two-dimensional aretriggered sequentially as described above. Other discrete x-ray sourcesthat currently exist or that may be developed in the future may also beemployed in a substantially similar manner, and are within the scope ofthe present invention as described herein and as claimed in any appendedclaims.

The use of x-ray source arrays of this type for this application may beparticularly advantageous for the following reasons:

-   -   The x-ray source can be very compact, especially in the        dimension along the line of x-ray emission.    -   Use of a linear array of x-ray beams advantageously reduces        image distortion associated with single point sources.    -   This approach to generating x-rays provides flexibility in image        acquisition, geometry and footprint that is far superior to        current single point x-ray source-based systems.    -   By using sequential triggering of the linear array of x-ray        sources, a backscatter image can be acquired without cross-talk        between sources.    -   This invention, when applied in a configuration that        simultaneously captures two or more views of the person being        scanned, advantageously enhances the throughput of inspected        subjects.

Another embodiment of the invention is now described with reference toFIG. 10A. Sets of carbon nanotube x-ray sources 1110 configured aslinear arrays 1111, or as a two-dimensional array, are placed above (asshown) or at the sides of, a person 1112 being scanned. It is to beunderstood that a person is shown as a representative object ofinspection, but that the apparatus and methods taught herein are ofvaluable applicability to any object, whether animate or inanimate.

Scatter detectors 1114, which may be backscatter or sidescatterdetectors, for example, are positioned to capture scattered x-rays. Theperson being scanned walks through the x-ray beams 1116 or istransported through by means such as a conveyor 1118 or people mover. Ahand-hold 1119 may also be provided. Separate sources 1110 may beactivated sequentially to provide spatial resolution in accordance withknown algorithms. FIG. 10B depicts subject 1112 in successive positionstraversing an inspection station that is designated generally by numeral1100. Inspection station 1100 has a front source 1160 and a back source1162, each of which may contain linear arrays, such as source 1111depicted in FIG. 10A, each of which is comprised of multiple discretex-ray sources disposed along an axis transverse to the page. Subject1112 either walks, or is conveyed by conveyor 1118, in such a manner asto have different parts of his/her person scanned by respective sources1160 and 1162 during the course of traversing the inspection station.

Yet a further embodiment of the present invention is shown in FIGS. 11Aand 11B, in a configuration approaching that of metal detectors incurrent use. As shown in the top view of FIG. 11B, x-ray source arrays1210 emit x-rays 1212, viewed most clearly in the front view of FIG. 6A.Array 1210 may be provided as a vertically disposed array. Each sourcein each array may be activated independent of the other sources in thearray in accordance with an embodiment of the present invention. X-rays1212 impinge upon subject 1112 as he/she traverses the inspectionstation, designated generally by numeral 1200. Radiation scattered bysubject 1112 or by objects carried or worn on the subject's person isdetected by scatter detectors 1220. Scatter detectors 1220 generatescatter signals on the basis of the penetrating radiation they detect,and the scatter signals are processed by processor 1230 to detect andidentify threat materials and objects in accordance with knownalgorithms, or, otherwise, to display a suitably processed image of theinspected subject at display monitor 1240. In either case, an image isgenerated, with the term “image,” as used herein and in any appendedclaims, signifying an ordered array of values corresponding to spatiallydistinct elements of the inspected object. Since the geometry minimizesdistortion and shadowing of the image data, automated detectiontechniques that rely on shape recognition greatly benefit from thereduced image distortion and shadowing. These advantages may also beapplied to conventional transmission and backscatter baggage systems.

Alternatively, electromagnetic scanners may be employed, such as scanner2104 (shown in FIG. 14) and those described in U.S. Pat. No. 6,421,420,issued Jul. 23, 2002 and entitled “Method and Apparatus for GeneratingSequential Beams of Penetrating Radiation,” which is incorporated hereinby reference. A source 2412 supplies a beam of charged particles 2140that are accelerated to a surface of a target 2160. Electromagnetic beamdirector 2418 can be any electromagnetic beam directing arrangement suchas magnetic or electrostatic yokes. Penetrating electromagneticradiation is emitted by target 2160 and pass through a collimator 2422disposed a specified distance from the target, thus producing sequentialparallel beams of radiation.

In cases where flying-spot systems are realized by mechanical means suchas rotating hoops and chopper wheels, these aforesaid criteria may bemet by synchronization of the motion of the mechanical chopper elements,biased by phase offsets. A system capable of such operation isdemonstrated in U.S. Pat. No. 7,400,701, hereby incorporated byreference herein in its entirety. Thus, for example, where collimatorsare rotated to define the path of emergent x-ray beam 2023, close-loopmotion controller systems known in the art may be employed to drive therotation of the collimators. The duty cycle is controlled by setting thefan aperture (the total sweep angle of a beam, i.e., the angle betweenexternal beams 2023 and 2024 of a single source), equal to 2π times theduty cycle. In systems where the emitted radiation can be controlledelectronically, any desired sequence of irradiation or range of sweepmay be set, without limitation, entirely by electronic or softwarecontrol.

By virtue of temporal sequencing which reduces or eliminates cross-talk,sources may be placed in greater proximity than otherwise possible. Inparticular, sources 2013, 2015 and 2017 may be disposed in a singleplane, which advantageously permits virtually simultaneous on/offcontrol of the x-rays regardless of the speed with which the object ispassing by the imagers.

The system described may advantageously provide for an image to bederived from the perspective of each successive source 2013, 2015 and2017, which emit beams 2023-2028. FIG. 12 shows an exemplary three-viewsystem 2010, with beams 2023, 2025, etc. each sweeping trajectories thatare coplanar.

The beams from each imager sweep in sequence, such that no more than oneimager is emitting radiation at a time. Thus, source (or ‘imager’) 2013sweeps its beam first. Radiation scattered from the object, asrepresented by rays 2044, is received by all of the detectors 2031-2036and transmitted to a processor 2040 to obtain images of the object,which may be conveyed through the system by an optional mechanizedconveyor 2029. The signals from each of the detectors are acquired asseparate channels by an acquisition system. This process is repeated foreach of the three imagers, creating “slices” of the object as it movesby.

Referring now to FIG. 13, a side view is shown of the arrangement ofFIG. 13, with elements designated by corresponding numbers. A slot 2050is shown through which the beam of source 2013 passes through segments2052 and 2054 of detector 2031 as object 2018 is scanned while moving ina lateral direction 2016.

The signals from the detectors can be selectively used to reconstruct animage of the object. Since scattered photons 2044 detected by detectors2033 and 2034 from source 2013 are as useful as scattered photons fromsource 2017, these same detectors can be shared among all sources, andresult in improved scatter collection with efficient use of the detectorhardware.

Embodiments of this invention, furthermore, may advantageously allowmulti-view Flying-Spot X-ray Scatter imaging to be practiced in asmaller operational footprint by eliminating cross talk, and by allowingcloser positioning of the individual imagers for each view. The closepositioning of these imagers (where an “imager” refers to a source, atleast one detector, and associated electronics and signal processing)may also allow sharing of scatter detectors between, or among, imagers,allowing more scatter collection for improved image quality, withefficient use of detector hardware.

In applications where scanning of selective regions of the object isdesired, co-planar positioning of the imagers allows simultaneous on/offcontrol of the x-rays regardless of the speed with which the object ispassing by the imagers. This greatly simplifies the design of thecontrol of x-ray emissions from each imager in the multi-view inspectionsystem, thus individual sequencing of x-ray emissions need not beperformed as is typically practiced in systems in which emission is notco-planar.

The described embodiments of the invention are intended to be merelyexemplary and numerous variations and modifications will be apparent tothose skilled in the art. All such variations and modifications areintended to be within the scope of the present invention as defined inthe appended claims.

1. An apparatus for ascertaining a material feature associated with asubject, the apparatus comprising: a first carriage and a secondcarriage, each carriage including a source including a collimatoradapted to produce a pencil beam of penetrating x-ray radiation incidenton the subject; at least one actuator adapted to displace each carriagewith respect to the subject in such a manner as to move the pencil beamwith respect to the subject in a direction having a vertical component;and at least one detector for detecting radiation produced by at leastone of the sources after backscattering of the radiation by the subject.2. An apparatus according to claim 1, wherein the at least one actuatoris adapted to synchronously displace each carriage with respect to thesubject in a direction having a vertical component.
 3. An apparatusaccording to claim 1, wherein a first detector is coupled to the firstcarriage.
 4. An apparatus according to claim 3, wherein a seconddetector is coupled to the second carriage.
 5. An apparatus according toclaim 1, wherein the first carriage includes a first scanner and thesecond carriage includes a second scanner, each scanner associated witha corresponding one of the sources and adapted to move the pencil beamof penetrating radiation produced by the corresponding source transverseto the direction of motion of such source's carriage.
 6. An apparatusaccording to claim 1, wherein the scanners are adapted to provideinterleaved beams.
 7. An apparatus according to claim 1, wherein thesource included on the first carriage and the source included on thesecond carriage produce substantially oppositely directed beams ofpenetrating radiation.
 8. An apparatus according to claim 1, whereineach source is an intermittently irradiating source.
 9. An apparatusaccording to claim 1 further comprising a processor for receiving asignal from the at least one detector and for producing an image basedat least on the signal.
 10. A method for inspecting a subjectcomprising: moving a first carriage, the first carriage having coupledto it a first source and a collimator adapted to produce a first pencilbeam of penetrating radiation incident on the subject, the firstcarriage moved in such a manner as to scan the first pencil beam ofpenetrating radiation in a direction having a vertical component; movinga second carriage, the second carriage having coupled to it a secondsource and a collimator adapted to produce a second pencil beam ofpenetrating radiation incident on the subject, the second carriage movedin such a manner as to scan the second pencil beam of penetratingradiation in a direction having a vertical component; detecting, with atleast one detector, radiation backscattered by the subject; generatingdetector output signals based on radiation received by the at least onedetector; and characterizing the subject on the basis of the detectoroutput signals.
 11. A method according to claim 10, wherein the act ofmoving the second carriage is synchronous with the act of moving thefirst carriage.
 12. A method according to claim 10, wherein at least afirst detector of the at least one detector is coupled to the firstcarriage.
 13. A method according to claim 12 wherein at least a seconddetector of the at least one detector is coupled to the second carriage.14. A method according to claim 10 further comprising moving the firstand the second carriages in respective directions, each of therespective directions having a vertical component.
 15. A methodaccording to claim 10 further comprising creating an image based onradiation detected by the at least one detector.
 16. A method accordingto claim 10, further comprising: scanning the beam of penetratingradiation produced by the source coupled to the second carriage in adirection transverse to the direction of motion of the carriages;generating detector output signals based on radiation received by the atleast one detector; and creating an image based on radiation detectedfrom the first and the second pencil beam.